1. Field of the Invention
The present invention is directed to a ballast for a discharge lamp, more particularly a high density discharge lamp such as a metal halide lamp and a mercury lamp.
2. Description of the Prior Art
As disclosed in Japanese Laid-Open Patent Publication No. 7-142182, a prior ballast for a discharge lamp is generally known to have a DC-to-DC converter supplying a DC voltage from a DC voltage source, a DC-to-AC inverter providing an AC voltage from the DC voltage source for operating the discharge lamp, a booster generating a boosted DC voltage, and a starter receiving the boosted voltage and providing a starting voltage of sufficiently high level for starting the lamp. The booster includes a capacitor which accumulates the boosted DC voltage to be supplied to the starter for developing the starting voltage. A problem remains in the ballast that, even if the ballast is deactivated as a consequence of that the discharge lamp fails to start due to absence of the lamp or the lamp reaching its end of operation life, the residual capacitance in the capacitor of the booster may cause the starter to develop the starting voltage or at least gives the boosted voltage to the starter, thereby giving unnecessary high voltage which may give undue stress to the components of the starter and create a possible electrical shock hazard to a personnel who accidentally touch the connection between the booster and the starter.